This table lists changes in blue
and suggestions in green. The
location of each
change and suggestion is specified by
book page number, text column, and paragraph (¶) in the column. The first line
of text in a column begins the first paragraph in that column even if the
first line begins in the middle of a sentence.

The integumentary system is made up of
the skin and the subcutaneous layer that
underlies it. This system makes up most of the external surface of
the body. Because of its position, the integumentary system is
always in direct contact with the external environment and lies
between it and the internal environment of the body. Therefore, this
system plays a major biological role in maintaining a person's
homeostasis and thus that person's happy and healthy survival. The
major functions of the integumentary system are serving as a barrier
between the body and its surroundings, providing information about
the external environment, regulating body temperature,
starting the process of vitamin D production, and actively defending
the body from harmful physical and biological factors. In
addition, because it is a highly visible system, it frequently
affects the social, psychological, and economic aspects of a
person's life.

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Gathering information about
conditions in and around the body is essential for survival. It is
the first step in negative feedback and
positive feedback systems that help maintain homeostasis.

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Since the integumentary system
is between most cells of the body and the external environment, it
can supply information about factors that might alter internal
conditions of the body even before those factors have an opportunity
to do so. For example, many
abundant nerve cells in the integument continuously monitor the
external environment and send messages to other parts of the nervous
system. As a result, the person knows much about the area
surrounding the body, including the location, size, shape, texture,
movement, and temperature of objects and materials (e.g., clothes,
furniture, water, air). Then the person can take steps to avoid or
correct any threatening features, perhaps before harm is done.
Information provided by nerve cells in the integumentary system can
also provide pleasure that can improve the quality of life. Examples
include enjoyment from physical touches (e.g., hugs, caresses) and
temperatures (e.g., cool breeze, warm blanket). In later parts of
this chapter, other types of cells are mentioned
that monitor conditions to initiate negative feedback or helpful
positive feedback activities contributing to homeostasis.

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Add new section as fifth
main function of the integumentary system.

Defense

The
integumentary system provides defense when components
assist actively in isolating, destroying or removing a harmful agent
from the body (e.g., splinter, poison ivy sap, bacteria, viruses,
cancer cells). Negative feedback (e.g., healing) and helpful
positive feedback (e.g., inflammation, immune reactions) are used in
defense activities. Defense prevents or limits damage from the
harmful agent in the integumentary system and reduces the risk of
damage in other body regions from agents that may spread (e.g.,
toxins, infection, cancer).

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Keratinocytes produce several
substances that help regulate inflammation and immune responses,
which are defense activities. The stratum corneum provides a
barrier against microbes; many chemicals, including water; and
abrasion. Though it is always being gradually
worn away at the outer surface, it is maintained by having
new keratin produced at the same rate by the next generation of
keratinocytes. The stratum corneum serves well as long as it remains
thick enough and is not broken by cuts,
tears, scrapes, or burns.